Gonadotropin Releasing Hormone ("GnRH", also known as Luteinizing Hormone Releasing Hormone, or "LHRH"), is of central importance to the regulation of fertility. Johnson M., Everitt B. Essential Reproduction, 3rd Edn. Blackwell Scientific Publications, 1988. In males and females, GnRH is released from the hypothalamus into the bloodstream and travels via the blood to the pituitary, where it induces the release of the gonadotropins, luteinizing hormone and follicle stimulating hormone, by gonadotrophs. These two gonadotropins, in turn, act upon the gonads, inducing steroidogenesis and gametogenesis. Steroids released from the gonads into the circulation subsequently act upon various tissues.
The gonadotropin hormonal cascade can be halted by neutralization of the biological activity of GnRH. Fraser H. M. Physiological Effects of Antibody to Leutenizing Hormone Releasing Hormone. In: Physiological Effects of Immunity Against Reproductive Hormones, Edwards and Johnson, Eds. Cambridge University Press, 1976. As a consequence of GnRH neutralization, the gonadotropins and gonadal steroids are not released into the blood and their biological activities are thereby eliminated. By eliminating the biological activity of GnRH, the hormonal regulation of fertility is interrupted and gametogenesis ceases. GnRH neutralization halts the production of gametes. GnRH neutralization is thus an effective means of contraception.
A number of important diseases are affected by gonadotropins and gonadal steroid hormones, particularly the gonadal steroids. Such diseases include breast cancer, uterine and other gynecological cancers, endometriosis, uterine fibroids, prostate cancer and benign prostatic hypertrophy, among others. Removal of the gonadal steroid hormonal stimuli for these diseases constitutes an important means of therapy. An effective method of accomplishing this is by neutralizing GnRH, the consequence of which is the elimination of gonadal steroids that induce and stimulate these diseases. McLachlan R. I., Healy D. L., Burger G. B. 1986. Clinical Aspects of LHRH Analogues in Gynaecology: a Review, British Journal of Obstetrics and Gynaecology, 93:431-454. Conn P. M., Crowley W. F. 1991. Gonadotropin-Releasing Hormone and Its Analogs, New England Journal of Medicine. 324:93-103. Filicori M., Flamigni C. 1988. GnRH Agonists and Antagonists, Current Clinical Status. Drugs. 35:63-82.
One effective means of neutralizing GnRH is the induction or introduction of anti-GnRH antibodies in the host or patient. Such antibodies can be induced by active immunization with GnRH immunogens or by passive immunization by administering anti-GnRH antibodies. Fraser H. M. Physiological Effects of Antibody to Leutenizing Hormone Releasing Hormone. In: Physiological Effects of Immunity Against Reproductive Hormones, Edwards and Johnson, Eds. Cambridge University Press, 1976. Since anti-GnRH antibodies can neutralize the biological activity of GnRH, immunization constitutes an important approach towards treating diseases dependent upon gonadal steroids and other reproductive hormones as well as a means to regulate mammalian fertility.
GnRH has the same amino acid sequence in all mammals (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GlyNH.sub.2) (SEQ ID NO: 1 in the Sequence Listing), thus a single immunogen would be effective in all mammalian species, including humans. Active immunization against GnRH, however, has not been practicable due to deficiencies associated with the GnRH immunogens. The prior art anti-GnRH immunogens are not of sufficient potency, and therefore must be administered repeatedly to induce effective levels of anti-GnRH antibodies. In addition, they have not proven to be reliable, in terms of inducing anti-GnRH antibodies in an acceptable portion of the immunized population.